1. Field of the Invention
The invention is concerned with a hydraulic motor and control system therefor and more particularly with improvements in the control system which allow the hydraulic motor to operate in any of a Float, a First position providing power in a first direction (e.g., a Raise position) or a Second position providing power in a second direction (e.g., a Lower position). Generally the system will also allow the hydraulic motor to operate in a Neutral (Hold) position. Such a control system is particularly advantageous when used with various types of earth working equipment such as, for example, a front loading loader, a dozer, a lift piston of a tractor-scraper and the like.
2. Prior Art
Control valves for hydraulic motors are known which provide Float, Neutral, Raise (first direction power) and Lower (second direction power) position. Further, a particular safety problem exists with prior art hydraulic motor control systems, which problem is that the pressure from the pump to the hydraulic motor of such a system may be suddenly cut off during Raise or Neutral operation due to breakage of the line therebetween, failure of the pump, or failure of the engine driving the pump. In such an instance and particularly when line breakage occurs, if the hydraulic motor is holding a load, e.g., in a raised position, the load can fall very quickly under the influence of gravity thus causing potentially great harm to the load itself and to the equipment.
The present invention provides a particular control system-hydraulic motor combination which eliminates this problem of a fast falling load but at the same time retains each of the Float, Neutral, Lower and Raise positions of operation for the control system and which further operates solely by mechanical means thus providing quick and positive action and shifting between the Float position, the Neutral position, the Raise position, and the Lower position.